Various methods for the preparation of copolyester-carbonates are described in U.S. Pat. Nos. 3,030,331, 3,169,121 and 3,207,814, all of which are hereby incorporated by reference. In addition, copending application Ser. No. 755,352, now abandoned, assigned to the same assignee as this case, discloses a method for preparing polyester carbonates by an interfacial polymerization process wherein the copolymers obtained contain both carboxylate and carbonate groups. Further, copending application Ser. No. 844,285, now U.S. Pat. No. 4,130,548 also assigned to the same assignee as this case, discloses a method for preparing copolyester-carbonates from a mixed polyanhydride ester of a dicarboxylic acid and a halogen carbonic acid ester of a polyhydroxy compound.
While these prior art methods are useful, they are not completely satisfactory as they either involve complex chemical reactions and costly equipment, or require expensive starting materials, or are time consuming and, therefore, uneconomical to manufacture.